1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device comprising a non-volatile storage element and a manufacturing method thereof.
2. Description of the Related Art
In a semiconductor device comprising a non-volatile storage element, if hydrogen or the like penetrates into an insulator of a capacitor after memory cells are formed, characteristics of the memory cells can be deteriorated. For example, hydrogen penetrated into a gate insulator of a memory cell transistor forms trap sites for electric charges. If electrons are trapped in the trap sites or electrons are released from the traps, then characteristics of the memory cell transistor fluctuate. In order to avoid such fluctuation, there is a technology which covers the memory cell transistor with a hydrogen barrier insulator.
With progress in miniaturization of a semiconductor device, it has been demanded to reduce resistivity of a silicide layer formed in an upper part of a gate electrode in order to achieve further miniaturization and higher speed operation of the semiconductor device. In general, the hydrogen barrier insulator is formed to cover the memory cell transistor after forming the silicide layer. Jpn. Pat. Appln. KOKAI Publication No. 2004-241780 discloses an example of a semiconductor device having such a configuration. In the configuration, a memory cell transistor having tungsten silicide (WSi) layer on the top of the gate electrode is covered with a stress buffering oxide film, and a space between adjacent memory cell transistors is filled with a spacer film (e.g., silicon nitride (Si3N4) film). After etching-back the spacer film, entire memory cells including an upper surface of the etched back spacer film are covered with an etching stopper film (e.g., Si3N4 film). The etching stopper film also has a function as a hydrogen barrier insulator. More specifically, the hydrogen barrier insulator is formed above the gate electrode without contacting with the silicide layer formed in the top of the gate electrode.
Silicide having a lower resistivity, e.g., cobalt silicide (CoSi) is apt to be deteriorated during a high-temperature heat treatment as compared with a conventional silicide material, e.g., WSi. If the hydrogen barrier insulator, e.g., Si3N4 film, is formed after forming CoSi, then CoSi tends to aggregate during a high-temperature CVD process for forming the Si3N4 film, thereby resulting in a problem such as an increase in a resistivity or disconnection of the silicide layer in an extreme case.